The present invention relates generally to methods and machines for manufacturing composite tubular articles such as golf club shafts and the like.
Composite articles comprise reinforcing fibers embedded in a matrix. Graphite, boron, glass, KEVLAR and other fibers are well-known. Epoxy is a well-known matrix. The fibers may be aggregated in woven textiles or in strips or sheets in which the fibers are uniaxial, i.e., unidirectionally aligned. Strips impregnated with epoxy resin are commonly known as xe2x80x9cpre-pregxe2x80x9d strips. To manufacture a composite article, pre-preg strips are laid upon or wrapped around a form or bonding tool in multiple plies. Although, to a certain extent, the somewhat tacky resin adheres the pre-preg strips to the bonding tool, the strips quickly begin to separate from the bonding tool, particularly if the tool is non-planar or contoured. Separation of the pre-preg from the bonding tool will not only result in a composite article that is aesthetically undesirable because it does not correspond to the contours of the bonding tool, but will also result in structural defects in the article. Adhesion can be facilitated by pre-heating the bonding tool, but to maintain the pre-preg strips firmly in contact with the surface of the bonding tool during subsequent curing processes the assembly is typically tightly enclosed in a wrapping material, such as cellophane film or a plastic bag. The wrapped assembly is then cured at a high temperature, typically between 180 and 350 degrees Fahrenheit. If the wrapping material by itself would not otherwise adequately secure the pre-preg in contact with the bonding tool during curing, the assembly may be cured in an autoclave at both a high temperature and a high pressure. The pressure collapses the bag-like wrapper and thus presses the pre-preg firmly against the surface of the bonding tool. When curing is complete, the wrapper is removed from the assembly, and the resulting composite article is removed from the bonding tool.
Golf club shafts, fishing rods and other tubular articles may be fabricated using composite materials. To fabricate such tubular articles, the pre-preg strips may be wrapped around a cylindrical bonding tool or mandrel and then cured as described above. As with any composite manufacturing process, it is desirable to ensure that the pre-preg adheres to the mandrel and conforms precisely to its taper. Rolling machines are known that comprise two generally parallel planar surfaces or platens, between which the mandrel is rolled while wrapping it with pre-preg strips. The angle between the platens may be adjusted off-parallel to conform to the mandrel taper. A drive mechanism moves the lower platen with respect to the upper platen and thereby rolls a mandrel sandwiched between them. Pre-preg strips fed between the rolling mandrel and one of the platens will thus generally be securely wrapped around the mandrel if the mandrel has a uniform taper. The mandrel may be pre-heated to facilitate adhesion of the pre-preg.
Although the above-described process is adequate for fabricating tubular composite articles having uniform tapers, the planar platens cannot roll pre-preg strips tightly against the surface of a mandrel having a non-uniform taper or other complex contours. The platens of rolling machines may therefore be provided with a resilient surface such as a rubber pad. Nevertheless, the rubber pads do not exert a sufficiently uniform pressure against the mandrel; more pressure is exerted on sections of the mandrel having greater diameters than is exerted on sections of the mandrel having smaller diameters. To further increase pressure uniformity, the platens may be divided into narrow sections that can be likened to the keys of a piano. Each piano key-like section is resiliently cushioned independently of the other sections. Nevertheless, a uniform pressure cannot be exerted against a mandrel having a diameter that changes over a distance less than the width of a single key-like section.
It would be desirable to provide an apparatus for rolling pre-preg around a mandrel having complex contours that maximizes pressure uniformity. These problems and deficiencies are clearly felt in the art and are solved by the present invention in the manner described below.
The present invention includes an apparatus for wrapping pre-preg strips around a mandrel and a method for using the apparatus to produce composite tubular articles, such as golf club shafts and fishing rod bodies. As used herein, the word xe2x80x9ctubularxe2x80x9d includes any shape that is symmetrical about an axis of rotation and is not limited to substantially elongated tubular shapes such as golf club shafts and fishing rod bodies.
The apparatus comprises a frame, a drive mechanism for rotating a mandrel, at least two spindles mounted to the frame, a tensioner, and a belt extending between the first and second spindles. The belt travels over the spindles, and the spindles guide the belt through changes in its direction of travel. The mandrel is mounted in the drive mechanism in contact with the belt, which changes its direction of travel around the mandrel. In an exemplary embodiment, the lower surface of the belt bears against upper portions of the spindles, and the mandrel contacts the upper surface of the belt. (Directional terms such as xe2x80x9cupperxe2x80x9d and xe2x80x9clowerxe2x80x9d are used herein only for the purpose of clarity to provide a frame of reference, and are not intended to refer to any specific orientation with respect to the Earth.) The belt is made of a material that is sufficiently flexible or pliable to conform to contours of the mandrel. As the drive mechanism rotates the mandrel, pre-preg sheets are fed between the mandrel and the belt and are thereby wrapped around the mandrel. The belt presses the pre-preg sheets against the mandrel. The wrapped mandrel may then be removed from the apparatus and cured in any suitable manner known in the art to produce a composite tubular article.
In the exemplary embodiment, the belt is not a continuous loop; rather, the ends of the belt are connected to the tensioner. Nevertheless, in certain embodiments, the belt may be continuous. The tensioner may comprise any suitable device or devices for maintaining tension in the belt relative to the first and second spindles. In the exemplary embodiment, the tensioner comprises resilient cords that connect the ends of the belt to each other and further comprises a third spindle. The belt and cords pass around the three spindles, and the third spindle is selectably movable toward and away from the first and second spindles to release and apply tension, respectively. Moving the third spindle to the position in which the belt is relaxed facilitates insertion and removal of the mandrel. In certain other embodiments, however, the tensioner may comprise other types of resilient members or other types of movable spindles. For example, although in the exemplary embodiment the movable spindle portion of the tensioner comprises a third spindle and a mechanism that moves the third spindle toward and away from the first and second spindles, in other embodiments a movable spindle type of tensioner may comprise mechanisms for moving any one or more of the spindles with respect to other spindles. The mechanisms may include a mechanical actuator, such as a pneumatic cylinder and/or may include a resilient member, such as a spring. Similarly, although in the exemplary embodiment the resilient portion of the tensioner comprises cords that connect the ends of the belt, in other embodiments a resilient type of tensioner may comprise one or more resilient members connected to the spindles or resilient material integral to the belt. In still other embodiments, the tensioner may comprise suitable combinations of the above-described tensioners.
The spindles may comprise any suitable devices between which a belt loop can extend and that facilitate movement of the belt relative to the apparatus frame. The word xe2x80x9cloopxe2x80x9d refers to the portion of the belt that contacts the mandrel when the apparatus is used and should not be construed to imply limitations regarding the shape, length or tension of this belt portion. The spindles may either be rotatably or non-rotatably mounted with respect to the frame. In an exemplary embodiment, the spindles comprise rotatably mounted rollers over which the belt passes. In other embodiments, however, they may comprise non-rotatably mounted projections or guides made of a low-friction material over which the belt slides. A spindle may comprise multiple portions that cooperate with the belt independently of one another. For example, a spindle may comprise multiple rollers mounted on a shaft. The apparatus may comprise different types of spindles in combination with one another.
The foregoing, together with other features and advantages of the present invention, will become more apparent when referring to the following specification, claims, and accompanying drawings.